Retinal prosthesis and method of manufacturing a retinal prosthesis

ABSTRACT

An improved package and configuration for an implantable retinal prosthesis includes an electrode array suitable to be mounted in close proximity to a retina, an electronics package, and an inductive receiving coil mounted next to each other on a strap surrounding the sclera so that the height above the sclera of the prosthesis is minimized.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/385,315,entitled “Retinal Prosthesis and Method of Manufacturing a RetinalProsthesis”, filed Mar. 20, 2006, which claims benefit of U.S.Provisional Patent application Ser. No. 60/675,980, filed on Apr. 28,2005, entitled “Implantable Chip Scale Package and Low Profile OcularMount,” the disclosure of which is incorporated herein by reference.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support under grant No.R24EY12893-01, awarded by the National Institutes of Health. Thegovernment has certain rights in the invention.

This application is related to, but not dependent on, U.S. patentapplication Ser. No. 09/823,464 for Method and Apparatus for ProvidingHermetic Feedthroughs filed Mar. 30, 2001; Ser. No. 10/174,349 forBiocompatible Bonding Method and Electronics Package Suitable forImplantation filed Jun. 17, 2002; Ser. No. 10/236,396 for BiocompatibleBonding Method and Electronics Package Suitable for Implantation filedSep. 6, 2002; Ser. No. 10/820,240 for Retinal Prosthesis with SideMounted Inductive Coil filed Apr. 6, 2004; Ser. No. 11/206,482 forPackage for an Implantable Medical Device filed Aug. 17, 2005 and Ser.No. 11/207,644 for Flexible Circuit Electrode Array filed Aug. 19, 2005all of which are assigned to a common assignee and incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention is generally directed to neural stimulation andmore specifically to an improved hermetic package for an implantableneural stimulation device.

BACKGROUND OF THE INVENTION

In 1755 LeRoy passed the discharge of a Leyden jar through the orbit ofa man who was blind from cataract and the patient saw “flames passingrapidly downwards.” Ever since, there has been a fascination withelectrically elicited visual perception. The general concept ofelectrical stimulation of retinal cells to produce these flashes oflight or phosphenes has been known for quite some time. Based on thesegeneral principles, some early attempts at devising prostheses foraiding the visually impaired have included attaching electrodes to thehead or eyelids of patients. While some of these early attempts met withsome limited success, these early prosthetic devices were large, bulkyand could not produce adequate simulated vision to truly aid thevisually impaired.

In the early 1930's, Foerster investigated the effect of electricallystimulating the exposed occipital pole of one cerebral hemisphere. Hefound that, when a point at the extreme occipital pole was stimulated,the patient perceived a small spot of light directly in front andmotionless (a phosphene). Subsequently, Brindley and Lewin (1968)thoroughly studied electrical stimulation of the human occipital(visual) cortex. By varying the stimulation parameters, theseinvestigators described in detail the location of the phosphenesproduced relative to the specific region of the occipital cortexstimulated. These experiments demonstrated: (1) the consistent shape andposition of phosphenes; (2) that increased stimulation pulse durationmade phosphenes brighter; and (3) that there was no detectableinteraction between neighboring electrodes which were as close as 2.4 mmapart.

As intraocular surgical techniques have advanced, it has become possibleto apply stimulation on small groups and even on individual retinalcells to generate focused phosphenes through devices implanted withinthe eye itself. This has sparked renewed interest in developing methodsand apparati to aid the visually impaired. Specifically, great efforthas been expended in the area of intraocular retinal prosthesis devicesin an effort to restore vision in cases where blindness is caused byphotoreceptor degenerative retinal diseases; such as retinitispigmentosa and age related macular degeneration which affect millions ofpeople worldwide.

Neural tissue can be artificially stimulated and activated by prostheticdevices that pass pulses of electrical current through electrodes onsuch a device. The passage of current causes changes in electricalpotentials across visual neuronal membranes, which can initiate visualneuron action potentials, which are the means of information transfer inthe nervous system.

Based on this mechanism, it is possible to input information into thenervous system by coding the sensory information as a sequence ofelectrical pulses which are relayed to the nervous system via theprosthetic device. In this way, it is possible to provide artificialsensations including vision.

One typical application of neural tissue stimulation is in therehabilitation of the blind. Some forms of blindness involve selectiveloss of the light sensitive transducers of the retina. Other retinalneurons remain viable, however, and may be activated in the mannerdescribed above by placement of a prosthetic electrode device on theinner (toward the vitreous) retinal surface (epiretinal). This placementmust be mechanically stable, minimize the distance between the deviceelectrodes and the visual neurons, control the electronic fielddistribution and avoid undue compression of the visual neurons.

In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrodeassembly for surgical implantation on a nerve. The matrix was siliconewith embedded iridium electrodes. The assembly fit around a nerve tostimulate it.

Dawson and Radtke stimulated cat's retina by direct electricalstimulation of the retinal ganglion cell layer. These experimentersplaced nine and then fourteen electrodes upon the inner retinal layer(i.e., primarily the ganglion cell layer) of two cats. Their experimentssuggested that electrical stimulation of the retina with 30 to 100 μAcurrent resulted in visual cortical responses. These experiments werecarried out with needle-shaped electrodes that penetrated the surface ofthe retina (see also U.S. Pat. No. 4,628,933 to Michelson).

The Michelson '933 apparatus includes an array of photosensitive deviceson its surface that are connected to a plurality of electrodespositioned on the opposite surface of the device to stimulate theretina. These electrodes are disposed to form an array similar to a “bedof nails” having conductors which impinge directly on the retina tostimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describesspike electrodes for neural stimulation. Each spike electrode piercesneural tissue for better electrical contact. U.S. Pat. No. 5,215,088 toNorman describes an array of spike electrodes for cortical stimulation.Each spike pierces cortical tissue for better electrical contact.

The art of implanting an intraocular prosthetic device to electricallystimulate the retina was advanced with the introduction of retinal tacksin retinal surgery. De Juan, et al. at Duke University Eye Centerinserted retinal tacks into retinas in an effort to reattach retinasthat had detached from the underlying choroid, which is the source ofblood supply for the outer retina and thus the photoreceptors. See,e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). Theseretinal tacks have proved to be biocompatible and remain embedded in theretina, and choroid/sclera, effectively pinning the retina against thechoroid and the posterior aspects of the globe. Retinal tacks are oneway to attach a retinal electrode array to the retina. U.S. Pat. No.5,109,844 to de Juan describes a flat electrode array placed against theretina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayundescribes a retinal prosthesis for use with the flat retinal arraydescribed in de Juan.

US Patent Application 2003/0109903 to Berrang describes a Low profilesubcutaneous enclosure, in particular and metal over ceramic hermeticpackage for implantation under the skin.

SUMMARY OF THE INVENTION

The present invention is an improved hermetic package for implantationin the human body. The implantable device of the present inventionincludes an electrically non-conductive substrate including electricallyconductive vias through the substrate. A circuit is flip-chip bonded toa subset of the vias. A second circuit is wire bonded to another subsetof the vias. Finally, a cover is bonded to the substrate such that thecover, substrate and vias form a hermetic package.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the implanted portion of the preferredretinal prosthesis.

FIG. 2 is a side view of the implanted portion of the preferred retinalprosthesis showing the strap fan tail in more detail.

FIG. 3 is a perspective view of a partially built package showing thesubstrate, chip and the package wall.

FIG. 4 is a perspective view of the hybrid stack placed on top of thechip.

FIG. 5 is a perspective view of the partially built package showing thehybrid stack placed inside.

FIG. 6 is a perspective view of the lid to be welded to the top of thepackage.

FIG. 7 is a view of the completed package attached to an electrodearray.

FIG. 8 is a cross-section of the package.

FIG. 9 is a perspective view of the implanted portion of the preferredretinal prosthesis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

The present invention is an improved hermetic package for implantingelectronics within a body. Electronics are commonly implanted in thebody for neural stimulation and other purposes. The improved packageallows for miniaturization of the package which is particularly usefulin a retinal or other visual prosthesis for electrical stimulation ofthe retina.

FIG. 1 shows a perspective view of the implanted portion of thepreferred retinal prosthesis. A flexible circuit 1 includes a flexiblecircuit electrode array 10 which is mounted by a retinal tack (notshown) or similar means to the epiretinal surface. The flexible circuitelectrode array 10 is electrically coupled by a flexible circuit cable12, which pierces the sclera in the pars plana region, and iselectrically coupled to an electronics package 14, external to thesclera. Further an electrode array fan tail 15 is formed of moldedsilicone and attaches the electrode array cable 12 to a molded body 18to reduce possible damage from any stresses applied during implantation.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16, receiving signals from a primary inductive coil 17.Preferably the secondary inductive coil 16 is made from wound wire.Alternatively, the secondary inductive coil 16 may be made from aflexible circuit polymer sandwich with wire traces deposited betweenlayers of flexible circuit polymer. The electronics package 14 andsecondary inductive coil 16 are held together by the molded body 18. Themolded body 18 holds the electronics package 14 and secondary inductivecoil 16 end to end. This is beneficial as it reduces the height theentire device rises above the sclera. The design of the electronicpackage (described below) along with a molded body 18 which holds thesecondary inductive coil 16 and electronics package 14 in the end to endorientation minimizes the thickness or height above the sclera of theentire device. This is important to minimize any obstruction of naturaleye movement.

The molded body 18 may also include suture tabs 20. The molded body 18narrows to form a strap 22 which surrounds the sclera and holds themolded body 18, secondary inductive coil 16, and electronics package 14in place. The molded body 18, suture tabs 20 and strap 22 are preferablyan integrated unit made of silicone elastomer. Silicone elastomer can beformed in a pre-curved shape to match the curvature of a typical sclera.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 16 and molded body 18 are preferably ovalshaped. A strap 22 can better support an oval shaped secondary inductivecoil 16.

Further it is advantageous to provide a sleeve or coating 50 thatpromotes healing of the sclerotomy 48. Polymers such as polyimide, whichmay be used to form the flexible circuit cable 12 and flexible circuitelectrode array 10, are generally very smooth and do not promote a goodbond between the flexible circuit cable 12 and scleral tissue. A sleeveor coating of polyester, collagen, silicon, GORETEX®, or similarmaterial would bond with scleral tissue and promote

It should be noted that the entire implant is attached to and supportedby the sclera. An eye moves constantly. The eye moves to scan a sceneand also has a jitter motion to improve acuity. Even though such motionis useless in the blind, it often continues long after a person has losttheir sight. By placing the device under the rectus muscles with theelectronics package in an area of fatty tissue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 2 shows a side view of the implanted portion of the retinalprosthesis, in particular emphasizing the strap fan tail 24. Further, ahook 28 is molded into the strap 22 just beyond the end of the fan tail24. When implanting the retinal prosthesis, it is necessary to pass thestrap 22 under the eye muscles to surround the sclera. A surgical toolcan be used against the hook 28 to push the strap 22 under the rectusmuscles. The secondary inductive coil 16 and the moulded body 18 mustfollow the strap 22 under the lateral rectus muscle on the side of thesclera. The implanted portion of the retinal prosthesis is verydelicate. It is easy to tear the molded body 18 or break wires in thesecondary inductive coil 16 or electrode array cable 12. In order toallow the molded body 18 to slide smoothly under the lateral rectusmuscle, the molded body 18 is shaped in the form of a strap fan tail 24on the end opposite the electronics package 14.

Referring to FIG. 3, the hermetic electronics package 14 is composed ofa ceramic substrate 60 brazed to a metal case wall 62 which is enclosedby a laser welded metal lid 84. The metal of the wall 62 and metal lid84 may be any biocompatible metal such as Titanium, niobium, platinum,iridium, palladium or combinations of such metals. The ceramic substrateis preferably alumina but may include other ceramics such as zirconia.The ceramic substrate 60 includes vias (not shown) made frombiocompatible metal and a ceramic binder using thick-film techniques.The biocompatible metal and ceramic binder is preferably platinum flakesin a ceramic paste or frit which is the ceramic used to make thesubstrate. After the vias have been filled, the substrate 60 is firedand lapped to thickness. The firing process causes the ceramic tovitrify biding the ceramic of the substrate with the ceramic of thepaste forming a hermetic bond. Thin-film metallization 66 is applied toboth the inside and outside surfaces of the ceramic substrate 60 and anASIC (Application Specific Integrated Circuit) integrated circuit chip64 is bonded to the thin film metallization on the inside of the ceramicsubstrate 60.

The inside thin film metallization 66 includes a gold layer to allowelectrical connection using wire bonding. The inside film metallizationincludes preferably two to three layers with a preferred gold top layer.The next layer to the ceramic is a titanium or tantalum or mixture oralloy thereof. The next layer is preferably palladium or platinum layeror an alloy thereof. All these metals are biocompatible. The preferredmetallization includes a titanium, palladium and gold layer. Gold is apreferred top layer because it is corrosion resistant and can be coldbonded with gold wire.

The outside thin film metallization includes a titanium adhesion layerand a platinum layer for connection to platinum electrode array traces.Platinum can be substituted by palladium or palladium/platinum alloy. Ifgold-gold wire bonding is desired a gold top layer is applied.

The package wall 62 is brazed to the ceramic substrate 60 in a vacuumfurnace using a biocompatible braze material in the braze joint.Preferably, the braze material is a nickel titanium alloy. The brazetemperature is approximately 1000° Celsius. Therefore the vias and thinfilm metallization 66 must be selected to withstand this temperature.Also, the electronics must be installed after brazing. The chip 64 isinstalled inside the package using thermocompression flip-chiptechnology. The chip is underfilled with epoxy to avoid connectionfailures due to thermal mismatch or vibration.

Referring to FIGS. 4 and 5, off-chip electrical components 70, which mayinclude capacitors, diodes, resistors or inductors (passives), areinstalled on a stack substrate 72 attached to the back of the chip 64,and connections between the stack substrate 72 and ceramic substrate 60are made using gold wire bonds 82. The stack substrate 72 is attached tothe chip 64 with non-conductive epoxy, and the passives 70 are attachedto the stack substrate 72 with conductive epoxy.

Referring to FIG. 6, the electronics package 14 is enclosed by a metallid 84 that, after a vacuum bake-out to remove volatiles and moisture,is attached using laser welding. A getter (moisture absorbent material)may be added after vacuum bake-out and before laser welding of the metallid 84. The metal lid 84 further has a metal lip 86 to protectcomponents from the welding process and further insure a good hermeticseal. The entire package is hermetically encased. Hermeticity of thevias, braze, and the entire package is verified throughout themanufacturing process. The cylindrical package was designed to have alow profile to minimize its impact on the eye when implanted.

The implant secondary inductive coil 16, which provides a means ofestablishing the inductive link between the external video processor(not shown) and the implanted device, preferably consists of gold wire.The wire is insulated with a layer of silicone. The secondary inductivecoil 16 is oval shaped. The conductive wires are wound in definedpitches and curvature shape to satisfy both the electrical functionalrequirements and the surgical constraints. The secondary inductive coil16, together with the tuning capacitors in the chip 64, forms a parallelresonant tank that is tuned at the carrier frequency to receive bothpower and data.

Referring to FIG. 7, the flexible circuit 1, includes platinumconductors 94 insulated from each other and the external environment bya biocompatible dielectric polymer 96, preferably polyimide. One end ofthe array contains exposed electrode sites that are placed in closeproximity to the retinal surface 10. The other end contains bond pads 92that permit electrical connection to the electronics package 14. Theelectronic package 14 is attached to the flexible circuit 1 using aflip-chip bumping process, and epoxy underfilled. In the flip-chipbumping process, bumps containing conductive adhesive placed on bondpads 92 and bumps containing conductive adhesive placed on theelectronic package 14 are aligned and melted to build a conductiveconnection between the bond pads 92 and the electronic package 14. Leads76 for the secondary inductive coil 16 are attached to gold pads 78 onthe ceramic substrate 60 using thermal compression bonding, and are thencovered in epoxy. The electrode array cable 12 is laser welded to theassembly junction and underfilled with epoxy. The junction of thesecondary inductive coil 16, array 1, and electronic package 14 areencapsulated with a silicone overmold 90 that connects them togethermechanically. When assembled, the hermetic electronics package 14 sitsabout 3 mm away from the end of the secondary inductive coil.

Since the implant device is implanted just under the conjunctiva it ispossible to irritate or even erode through the conjunctiva. Erodingthrough the conjunctiva leaves the body open to infection. We can doseveral things to lessen the likelihood of conjunctiva irritation orerosion. First, it is important to keep the over all thickness of theimplant to a minimum. Even though it is advantageous to mount both theelectronics package 14 and the secondary inductive coil 16 on thelateral side of the sclera, the electronics package 14 is mounted higherthan, but not covering, the secondary inductive coil 16. In other wordsthe thickness of the secondary inductive coil 16 and electronics packageshould not be cumulative.

It is also advantageous to place protective material between the implantdevice and the conjunctiva. This is particularly important at thesclerotomy 48, where the thin film electrode cable 12 penetrates thesclera. The thin film electrode array cable 12 must penetrate the sclerathrough the pars plana, not the retina. The sclerotomy 48 is, therefore,the point where the device comes closest to the conjunctiva. Theprotective material can be provided as a flap attached to the implantdevice or a separate piece placed by the surgeon at the time ofimplantation. Further material over the sclerotomy 48 will promotehealing and sealing of the sclerotomy 48. Suitable materials includeDACRON®, TEFLON®, GORETEX® (ePTFE), TUTOPLAST® (sterilized sclera),MERSILENE® (polyester) or silicone.

Referring to FIG. 8, the package 14 contains a ceramic substrate 60,with metallized vias 65 and thin-film metallization 66. The package 14contains a metal case wall 62 which is connected to the ceramicsubstrate 60 by braze joint 61. On the ceramic substrate 60 an underfill69 is applied. On the underfill 69 an integrated circuit chip 64 ispositioned. On the integrated circuit chip 64 a ceramic hybrid substrate68 is positioned. On the ceramic hybrid substrate 68 passives 70 areplaced. Wirebonds 67 are leading from the ceramic substrate 60 to theceramic hybrid substrate 68. A metal lid 84 is connected to the metalcase wall 62 by laser welded joint 63 whereby the package 14 is sealed.

FIG. 9 shows a perspective view of the implanted portion of thepreferred retinal prosthesis which is an alternative to the retinalprosthesis shown in FIG. 1.

The electronics package 14 is electrically coupled to a secondaryinductive coil 16. Preferably the secondary inductive coil 16 is madefrom wound wire. Alternatively, the secondary inductive coil 16 may bemade from a flexible circuit polymer sandwich with wire traces depositedbetween layers of flexible circuit polymer. The electronics package 14and secondary inductive coil 16 are held together by the molded body 18.The molded body 18 holds the electronics package 14 and secondaryinductive coil 16 end to end. The secondary inductive coil 16 is placedaround the electronics package 14 in the molded body 18. The molded body18 holds the secondary inductive coil 16 and electronics package 14 inthe end to end orientation and minimizes the thickness or height abovethe sclera of the entire device.

Accordingly, what has been shown is an improved retinal prosthesis.While the invention has been described by means of specific embodimentsand applications thereof, it is understood that numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is therefore tobe understood that within the scope of the claims, the invention may bepracticed otherwise than as specifically described herein.

1. A retinal prosthesis comprising a video capture device; a source ofpower; a primary inductive data transmission coil suitable to be placedoutside of the body and electrically coupled to said video capturedevice and said source of power and transmitting video information fromsaid video capture device; an electrode array suitable to be mounted inclose proximity to a retina; a strap suitable to surround the eye; ahermetic at least partially ceramic electronics package encasing activeand passive electronics and mounted on said strap; an electrical cablecoupling said electrode array to said hermetic at least partiallyceramic electronics package; wherein said electrical cable is suitableto pierce the pars plana region of the sclera; a secondary inductivedata transmission coil mounted on said strap next to, and coplanar with,said hermetic at least partially ceramic electronics package,electrically coupled to said hermetic at least partially ceramicelectronics package, suitable to be mounted to the side of a sclera andin close proximity to said primary inductive coil and receiving thevideo information from said primary inductive coil; wherein height abovethe sclera of said strap hermetic at least partially ceramic electronicspackage and coil is minimized.
 2. The retinal prosthesis according toclaim 1, further comprising suture tabs connected to said secondaryinductive coil suitable for attaching said secondary inductive coil tothe sclera.
 3. The retinal prosthesis according to claim 1, furthercomprising suture tabs connected to said hermetic at least partiallyceramic electronics package suitable for attaching said hermetic atleast partially ceramic electronics package to the sclera.
 4. Theretinal prosthesis according to claim 1, further comprising a fan tailconnected to said secondary inductive coil and to said strap tofacilitate to passing said strap and said secondary inductive coilthrough muscle tissue.
 5. The retinal prosthesis according to claim 1,further comprising a hook on said prosthesis suitable for engaging asurgical tool.
 6. The retinal prosthesis according to claim 1, whereinsaid cable and electrode array comprise metal traces sandwiched betweenthin polymer films.
 7. The retinal prosthesis according to claim 6,wherein said cable is folded to present the same side of said cable toboth said electronics package and the retina.
 8. The retinal prosthesisaccording to claim 1, wherein said secondary coil is substantially ovalshaped.
 9. The retinal prosthesis according to claim 1, wherein saidelectrode array is suitable to be placed in an epiretinal location. 10.The retinal prosthesis according to claim 1, wherein said secondaryinductive coil is a wound wire coil.
 11. The retinal prosthesisaccording to claim 1, wherein said primary coil is integrated in thetemple of a pair of glasses.
 12. A retinal prosthesis comprising: anelectrode array suitable to be mounted in close proximity to a retina; astrap suitable for surrounding an eye; a hermetic at least partiallyceramic electronics package encasing active and passive electronics andmounted on said strap; an electrical cable, suitable to pierce the parsplana region of the sclera, coupling said electrode array to saidhermetic at least partially ceramic electronics package; a secondaryinductive data transmission coil mounted on said strap next to andcoplanar with said electronics package, electrically coupled to saidelectronics package, and receiving video information; wherein heightabove the sclera of said strap electronics package and coil isminimized.
 13. The retinal prosthesis according to claim 12, furthercomprising a getter within said hermetic at least partially ceramicelectronics package.
 14. The retinal prosthesis according to claim 12,wherein said hermetic at least partially ceramic electronics package isformed of a ceramic base, including conductive vias and a metal cover.15. The retinal prosthesis according to claim 14, further comprisingwire bonds electrically coupling a flip-chip package to said conductivevias.
 16. The retinal prosthesis according to claim 12, wherein saidhermetic at least partially ceramic electronics package includes aflip-chip package.
 17. The retinal prosthesis according to claim 16,wherein said hermetic at least partially ceramic electronics packageincludes a stack substrate including discrete components bonded to saidflip-chip package.
 18. The retinal prosthesis according to claim 16,further comprising a polymer under fill under said flip-chip package.